The two drones, tail numbers WK042 and WK043, crashed within seven weeks of each other, in February and March this year. Both "remotely piloted aerial systems" (RPAS) were lost in Cardigan Bay, immediately west of West Wales Airport, Aberporth, causing the remaining 52 drones to be grounded for four months.

The Watchkeeper is undergoing lengthy flight testing with the Army. Initially proposed as a surveillance drone, the programme has achieved relatively little for the 12 years and ￡1.2bn+ spent on it, though the Bureau of Investigative Journalism found two years ago that the drones had seen a total of 146 hours of active duty – equating to two days' operational flying each.

WK042 was lost in the sea on February 3, according to the Defence Safety Authority's latest biannual report published this week. The drone was being flown from its ground station by a combined crew of Thales and UAV Tactical Systems (UAVTS) operators who were testing de-icing equipment. Historical weather data for Aberystwyth, around 20 miles north of Aberporth and also on the edge of Cardigan Bay, shows that temperatures on the day averaged about 9oC.

WK043 was lost on March 24 in the same area while being flown by a combination of Army, Thales and UAVTS operators, while a soldier was being trained to pilot the drone. Watchkeepers cannot be flown in the "stick and rudder" sense; instead, operators select waypoints on a map display and the drone flies itself towards them.

Though the MoD also operates other drones, including Predators bought from America, these seem to crash less often. However, an MQ-9 Reaper, serial number ZZ205, is now the subject of a formal service inquiry following an unspecified incident in August 2016.

We asked the MoD to comment on what type of investigation is being undertaken into the latest Watchkeeper crashes and why it did not come clean about the crashes when they first occurred. A spokesman for the department told us that no injury or loss of life had occurred and added: "We paused Watchkeeper flying for a short period whilst conducting initial investigations, but resumed flight trials in early July. Service inquiries into the specific incidents are ongoing as we look to learn all we can from the events."

A Watchkeeper operational field trial exercise has been taking place from West Wales Airport since mid-September and is due to end this Sunday, November 5. A company-sized unit from 47 Regiment, Royal Artillery, has been flying its drones from the Aberporth airfield.

A safety and reputational risk in the making

Watchkeeper is a relatively old programme (as this authoritative history by top blogger Think Defence explains) that has absorbed large sums of public money for a return that is largely invisible to the taxpayer.

Previous crashes highlighted Watchkeeper's poor controllability in marginal weather conditions and poor onboard software, in combination with its use of laser altimeters as a primary height sensor – a strange choice for aircraft operating in the wet and cloudy skies of Wales. While El Reg has sympathy for trainees cocking up a landing, this does not excuse the MoD for hiding behind self-regulation to pretend that all is well.

As Watchkeepers do make flights over the UK mainland as well as the sea, the MoD must be open and transparent about when its unmanned aircraft crash and why. Civil aviation has long grasped this essential point and the Air Accidents Investigation Branch is proactive with publishing interim reports into civil aircraft crashes and malfunctions. In contrast, the Military Aviation Authority says very little on matters of public interest.

There is no justification for the MoD keeping quiet and hoping nobody notices just because these latest crashes were into the sea and didn't involve human victims. For all the public knows, the next Watchkeeper crash could result in one of these million-pound airframes landing in their back gardens – or even a built-up area. ?